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Flat-Tappet Cams and Worn Down Engines - The Perfect Storm

A high-energy magnet cemented on the drain plug provides an early warning of serious engine problems. It works. The first warning of a potential cam lobe failure was a metal "mud" made of fine particles clinging to the magnet. The cam wear problem was evident after the valve covers were removed, and one rocker arm was seen to be moving less than its companions.

Removal of the intake manifold and then removal of the suspected lifter confirmed the extent of the problem. The lifter was so worn down that it was visibly shorter, and the bottom of the lifter was worn into a concave surface with sharp edges. Its cam lobe was equally bad.

The wear pattern is a relatively straight band on these two other lifters, showing that they had stopped spinning. Flat-tappet lifters are designed to spin so that their crown wears evenly. If they stop spinning, cam failure is imminent. A likely contributing cause to this was use of synthetic oil, even though it was used only well after break-in.

The camshaft on this small-block '73 Corvette required removal of the radiator. Although the A/C condenser did not have to be removed, the left lower corner had to be lifted up over the headlight actuator to provide sufficient clearance. This may not be necessary on all models. Measure to see if there's 211/2 inches of clearance from the front of the block at the cam centerline. Remember, the fuel pump has to be removed because of its cam-operated pushrod.

The idler arm was lowered to permit removal of the oil pan. Although the timing cover can be wedged out without removing the pan, in this case, we wanted to clean out any metal debris and check the condition of the bearings. A significant amount of metal particles were found on the bottom of the pan, and even on the top of the oil pump pickup.

Good news, bad news. The crankshaft journals were not damaged, but the bearings showed some contamination by metallic particles. One factor that helped save the engine from further damage was that we were alerted early to a problem by the particles picked up by the magnetic drain plug.

This modification of the oil filter mount helped protect the rest of the engine from the metal particles. The oil bypass valve opening was cemented shut with an epoxy to prevent any oil from bypassing the filter. The valve was originally intended to prevent oil pressure from dropping if the filter became clogged, but it's unnecessary when the oil is changed frequently.

With the pan off, this was a good time to change a drippy rear main seal, particularly since the bearings were also being replaced. A common problem with a rear seal is that its lip can wear into the crankshaft, and this area is not cleaned when the crank is ground. Felpro solves this by offering an offset seal (PN BS 11829-1) that has the seal lip in a slightly different location.

The one-piece rubber oil pan gasket from Felpro has been praised by a number of rebuilders. It comes with clever plastic studs to hold the gasket in place on the block while the pan is being installed. Silicone gasket sealer is used only on the four corners. The '74-and-up pans used a different thickness end gasket.

The Comp Cams retro-roller lifters come in an assembled pair, connected by a link bar to prevent them from rotating. While flat-tappet rollers must rotate to ensure cam life, roller lifters absolutely must not rotate. Another notable difference is that used flat-tappet lifters should never be run on a different cam (or even a different lobe), while used roller lifters can be run on different cams.

Different pushrods are required with a retro-roller cam because the roller lifters are longer. Unlike flat-tappet lifters, pushrods can be reused after a cam change if their ends show no excessive wear, and if they are straight. Simply roll the pushrods on a plate of glass to check for bends. If a flat-tappet cam is used, mark the upper end of the pushrod so that it's easy to check that it's spinning.

Different pushrods are required with a retro-roller cam because the roller lifters are longer. Unlike flat-tappet lifters, pushrods can be reused after a cam change if their ends show no excessive wear, and if they are straight. Simply roll the pushrods on a plate of glass to check for bends. If a flat-tappet cam is used, mark the upper end of the pushrod so that it's easy to check that it's spinning.

If you think the lobes on the Comp Cams roller cam look meatier, you're right. Even though the duration and lift specs are similar to the flat tappet cam, the lobes are visibly wider at the top in profile on a roller cam.

If your car occasionally gives a puff of blue smoke upon starting or after letting off on a long exit ramp, this is the perfect time to change valveguide seals. Choices include the umbrella seal that moves up and down with the valve, the original factory o-ring, and varieties of positive seals. The seal on the right presses onto the head's valve boss; in this case machined down to 0.500-inch diameter.

Degreeing the cam is not essential, but it will ease any worries about a problem with the cam or the timing gear. With the heads on, degreeing takes a $10 TDC stop tool, and then buying or borrowing a $25 degree wheel and a dial indicator with base. An hour of work here can prevent diagnosis dilemmas or parts problems that are more costly in the future.

Installation of a cam thrust button is recommended when switching from a flat-tappet cam to a retro-roller cam. In a flat-tappet Corvette engine, the taper of the cam lobe exerts rearward pressure on the cam, as does the distributor gear that drives the oil pump. Comp Cams offers stamped-steel covers that look original, but are reinforced inside for the thrust button.

The roller lifters were soaked in motor oil and installed along with the valvesprings, rocker arms, and pushrods. The heads do not have to be removed to change valve-springs or valveguide seals; a bungee cord or air pressure can be used via the spark plug hole to hold the valve up.

The Comp Cams hydraulic roller lifters were adjusted to a half-turn down from zero lash. The intake manifold was temporarily installed earlier to ensure its gasket was properly sealed and positioned on the heads. Now it was time for the permanent installation of the manifold, and then the valve covers and distributor.

Here's another great aspect of installing a retro-roller cam-just fire it up and drive off. There is no nerve-wracking break in procedure. And if the cam requires stiff valvesprings, there's no need to break in with softer springs and then reinstall the stiff springs after break-in.

Lube LessonsWatch out for the "gear" logo on conventional oils if you have a flat-tappet cam engine, such as Corvettes prior to 1987. Many of these oils have significantly reduced levels of special antiwear additives that can be critical to your engine's health.

Many "racing" oils still have adequate levels of the antiwear additives that can protect your flat-tappet cam. Don't worry if the label says "not for passenger cars," or explains that it may damage catalytic converters. This is not a problem for pre-'75 cars or other vehicles that don't have a catalytic converter.

Cam break-in oils are another good way to increase the level of the antiwear additives. The additives are concentrated so that adding these with each oil change can help protect your flat-tappet cam. They are available directly from the manufacturer, from local speed parts stores, or from on-line speed part suppliers.

New Lifter OptionsNitriding is a surface hardening process that also increases lubricity and can reduce the chance of premature cam failure, and, thereafter, extend cam and lifter life. Comp Cams offers this as an option on all their flat-tappet cam lobes and lifters. (Courtesy Comp Cams)

Tiny 0.012-inch holes, created in the hard lifter face by EDM, enable direct lubrication in one of an engine's worst lubrication problem areas. Comp Cams offers this as an option on many solid flat-tappet lifters. EDM-made holes are also available on solid roller lifters for greater lubrication of the roller. (Courtesy Comp Cams)

A lifter-bore grooving tool cuts a shallow groove down from the pressurized portion of the lifter bore. If your engine is apart, consider this an alternative to the EDM hole lifters. The groove ensures that oil runs down the lifter and onto the cam lobe. (Courtesy Comp Cams)

We take a look at three separate conditions that can put your cam's life in jeopardy and what you can do to prevent expensive engine work and what you can do to keep your engine from getting worn down. Corvette Fever Magazine » Read More